Exemplary embodiments of the invention relate to a spindle drive for the height adjustment of an electrically adjustable steering column having an adjustment spindle.
German patent document DE 196 41 152 A1 discloses a motor vehicle steering column unit that has been simplified in construction having a steering column housing and steering column arranged therein and an electrically driven adjustment device both for the longitudinal adjustment and for the inclination adjustment of the steering column. This adjustment device has, on the one hand, an electrical drive unit for the rotary drive of an adjustment spindle and, on the other hand, at least two spindle nuts arranged on the adjustment spindle and moveably mounted with axial bearings in the axial direction of the adjustment spindle. For the longitudinal movement and for the inclination movement, a switch device is provided per one adjustment mechanism as well as per movement direction, wherein a non-positive connection can be produced between the respective switch device and the spindle nut adjacent to the switch device.
Furthermore, German patent document DE 101 63 974 A1 discloses a motor vehicle steering unit having electrical inclination adjustment with an improved stiffness of the steering column in the vertical and horizontal direction. The motor vehicle steering unit has an inclination adjustment mechanism arranged on one side of the steering column to convert a rotary driving force of the electromotor into a straight-line movement, in order to thus set the inclination of the steering column, and a slide section arranged on the other side of the steering column, which is in sliding contact with a fixed side via a fitting, in order to thus be able to slide the steering column when setting the inclination. An adjustment spindle, referred to there as a screw shaft, is described for the inclination adjustment, which is mounted rotatably on its upper and lower ends in axial deep groove ball bearings. The upper bearing is fixed with a fixing screw, onto which a means is attached which prevents a release. By tightening this screw to a determined torsional moment, the bearings are pre-tensioned such that they securely support the screw shaft at the upper and lower end in the transverse direction.
Thus, until now, the adjustment spindles for the inclination mechanism of a steering column have been mounted in a floating manner with the axial deep groove ball bearings or needle bearings, which are tensioned with a plate spring or a nut.
Due to bearing play as a consequence of component and manufacturing tolerances, the adjustment spindle inserted between the bearings begins to oscillate in the operation during adjustment, which leads to undesired noises and to wear. In order to prevent this, until now, an exact alignment of the spindle drive has been necessary, requiring considerable effort.
In view of this prior art, exemplary embodiments of the present invention are directed to a spindle drive for an electrically adjustable steering column having an adjustment spindle for the height adjustment, which prevents the occurrence of oscillation in the adjustment operation and thus eliminates noise development and wear, and furthermore can be assembled with little effort.
Furthermore, exemplary embodiments of the present invention are directed to an electrically adjustable steering column having an adjustment spindle for the height adjustment, in which no oscillation occurs in the adjustment operation due to bearing play as a result of manufacturing and component tolerances, which lead to undesired noises and wear.
A spindle drive for height adjustment of an electrically adjustable steering column according to the invention comprises an adjustment spindle, which is mounted rotatably by means of two bearings. According to the invention, the adjustment spindle has two clamping elements, which have a centering cone on sides facing one another. Thus, the adjustment spindle is tensioned by means of the clamping elements on the two bearings, on the outer sides of which that face away from each other the clamping elements having the centering cones abut. For this purpose, the outer sides of the bearings are formed having a counter contour to the respectively abutting centering cone. Using the tensioning of the spindle on the bearings that is centered with the cones, no oscillation occurs in the adjustment operation due to the component and manufacturing tolerances. The noise occurring during adjustment can thus be reduced and also the waste can thus be reduced that is caused by spindle drives having undesired noise development during adjustment. As well as the noise optimization and reduction of the waste, the quality of the spindle drive is also improved as the wear in the height adjustment is reduced due to the prevention of the occurrence of oscillation.
One of the clamping elements can be formed by a widened head of the spindle, which is then formed with the centering cone on the corresponding side of the head facing the bearing.
The second clamping element can be formed by a lock ring attached to the end of the spindle facing away from the head and which is formed with the centering cone. During attachment of the lock ring, its centering cone is arranged facing the bearing.
This lock ring can be manufactured from a plastic or from an elastomer. The attachment onto the spindle can take place by pressing. Furthermore, the lock ring can bear an additional bearing support ring or a plate spring. Herein, for a lock ring made from elastomer it is preferred that the lock ring is vulcanized onto the bearing support ring or the plate spring.
Thus the assembly is significantly simplified in comparison to the prior art, as the elaborate alignment is omitted due to the centering cones, which tension the spindle on the bearings.
As an alternative to the lock ring as a second clamping element, a screw nut can be provided, which is attached to the end of the spindle facing away from the head and is formed with the centering cone. In order to prevent a release in the operation, the screw nut can have a self-locking thread.
For the two bearings mounting the adjustment spindle, contact ball bearings, preferably in an O-arrangement, can be used in particular, whereby the guiding of the spindle is further and more tightly centered.
Furthermore, the invention relates to an electrically adjustable steering column having a height adjustment mechanism, which comprises a spindle drive having an adjustment spindle mounted rotatably by means of two bearings. Due to the use of a spindle drive according to an embodiment according to the invention with the adjustment spindle tensioned by the centering cones of the clamping elements on the bearings, a steering column is created, the height adjustment of which is possible without undesired noises, and which has a longer service life of the adjustment mechanism due to the reduced wear as a consequence of the elimination of oscillation.